1. Field of the Invention
The present invention relates to a reverberation circuit for reverberating signals such as speech sound and music.
2. Prior Art
A reverberation circuit is a circuit for reverberating speech sound and music to create a sound field such as a concert hall and is widely used in, for example, a Karaoke device which is an apparatus for reproducing an instrumental part of a tune to which a user can sing.
FIG. 4 shows a general arrangement of a prior art reverberation circuit. In FIG. 4, the reverberation circuit includes an OP amp 1, a delay circuit 2, an input resistor 3, a feedback resistor 4, and a reverberation time adjusting resistor 5. The OP amp 1, the input resistor 3, and the feedback resistor 4 form a negative feedback inverting amplifier. The input signal to the inverting amplifier is amplified by the OP amp 1, then is delayed a predetermined amount of time by the delay circuit 2, and finally is fed back to the input terminal of the OP amp 1 through the reverberation time adjusting resistor 5, thereby circulating the delayed signal through the feedback loop to produce reverberated sound. The reverberation time can be adjusted at will be adjusting the reverberation adjusting resistor 5 to change the level of feedback signal.
The aforementioned reverberation circuit is of a sort of comb filter the period of which is the delay time of the delay circuit 2. Due to the comb filter characteristics, when the input signal to the reverberation circuit is cut off, the reverberated output sound decays much slower in high frequencies than in lower frequencies.
This problem is not so serious if the reverberation time T is short, but quite serious if a long reverberation time T is to be set, causing the trailing end of the reverberated sound to become "screechy" regardless of the types of sound and voice, e.g. men's voices and women's voices.